Leaks of fluids can occur in a commercial, industrial or residential environment. Fluid leaks are a problem and early detection can save significant expense and inconvenience. There are many ways to detect moisture, water or fluids and, in fact, many patents for devices or methods of detecting water, fluids or moisture have been previously issued. See, for example, U.S. Pat. No. 4,797,621 (Anderson et al.), U.S. Pat. No. 4,855,706 (Hauptly), and U.S. Pat. No. 4,910,998 (Willis et al.), incorporated herein by reference.
Several types of systems that provide water detection are:
1. Spot detection: An alarm is activated when fluid touches the sensor on the detector. PA1 2. Continuous cable detection: An alarm is activated when fluid touches any part of the cable. PA1 3. Continuous cable detection with indication: An alarm is activated when fluid has been detected, and it visually displays the distance from the control system to the leak. PA1 1. Center core cables tend to form a "set" and therefore they attempt to return to their original configuration if they are not restrained sufficiently. This makes installation difficult and time consuming. These cables also tend to be expensive. PA1 2. Flat cables with silk or polymer fibers that have wires embedded in the interior of the cable are difficult to install, as they will not curve due to their construction. In addition, they are difficult to dry out once fluids are in the cable. PA1 3. Cables held together with a weave of monofilament fibers are difficult to dry once they have become wet. In addition, moisture tends to be trapped in the fibers and can produce an accuracy problem in distance systems.
Spot Detection
Leak detection in the past was usually associated with piping, air-conditioners, chillers, cooling towers, and hot water heaters and tanks since these are the areas most likely to have plumbing leaks or overflow of drains.
Leak detection protection provided by a spot detector is a relatively inexpensive way to detect leaks. Most systems are a single point, spot detector, with two electrodes on a substrate (board), anchored to the floor. 24 VAC is used to activate a relay in the unit when current flows between the electrodes. Other systems used a resistor from the anode to the gate of an SCR that causes the SCR to fire when sufficient conduction has been detected between the posts of the device and remained on until the electrodes were no longer in the fluid. The biggest problem with the non-SCR type is that if one of the electrodes became grounded, the power supply would short out with catastrophic results.
Some less expensive types of spot detectors include the swelling sponge type, which physically close a contact when fluid causes the sponge to swell. The sponge has to be replaced after each occurrence of fluid being detected.
Spot detectors are very good at detecting leaks around devices especially if a dam has been constructed around the unit, otherwise all low points in the floor must be covered to ensure that fluid does not flow by the sensor undetected.
Continuous Cable Systems
Some leak detection systems use a detection cable system. The cable usually is routed around the perimeter of the unit and when a conductive material touches it at any point, the circuit is completed and the alarm sounds. This type of system makes the construction of a dam unnecessary. These devices are usually unreliable, from a false alarm point of view, during high humidity conditions, which exist in the discharge air of most air conditioners from time to time. Some systems also depend upon the air conditioner being on to detect a leak and if it is not operating for some reason, the ability for it to detect a leak is gone. These types of systems do not lend themselves to protecting areas which are far removed from the general area around the air conditioner. Cables under the floor, in high humidity conditions for long periods of time, tend to corrode and, in some instances, conductive polymers have been applied to such wires to prevent this corrosion. Even these polymers can become contaminated if left in water, while the system is in alarm, for a long period of time.
The cable can become damaged under the raised floor and may have to be removed to be repaired. This cable can also become contaminated with various chemicals and other fluids found under the raised floor. Installation and reinstallation of these cables can be expensive, especially if they have been routed over the entire floor area where a considerable number of power and data cables may be laid on top of the water sensing cable. It may also be necessary to shut down the computer to accomplish this task.
Continuous Cable with Indication
This system is similar to the one above except that the control system of the leak detection system has a visual readout that displays the distance in feet from the control system to the fluid that was detected. A system that has been properly installed and has a floor plan will allow the user to pinpoint where the system has detected a leak.
This type of system could interface with a computer and the length would be translated into an analog signal that would then be displayed on a CRT screen to show the location of the leak. The same problems exist with this system as exist with the continuous cable system discussed above.
Two technologies exist for these types of systems: resistance readings and Time Delay Reflectrometry (TDR). The TDR tends to be more expensive than the resistance reading systems. They do have one advantage under ideal conditions, i.e. they can read and record multiple leaks on the same cable. There are, however, some conditions under which the second location cannot be detected and that is if the first leak is large enough to keep the signal from reaching the end of the cable and returning to the control system. This type of cable is expensive to manufacture.
All of the foregoing cable systems have similar problems and these are:
There has not heretofore been provided a simple, efficient and reliable cable system for detecting a fluid on a surface (such as a floor, or a pipe, etc.) having the features and advantages provided by the present invention.